1. Field of the Invention
This invention relates to DC/DC and AC/DC power converters. More particularly, this invention relates to DC/DC and AC/DC power converters with soft switching in all of their semiconductor components.
2. Discussion of the Related Art
The boost converter topology has been extensively used in various AC/DC and DC/DC converter applications. In fact, the boost technology is used today in most front ends of DC/DC power supplies having power-factor correction (PFC). The boost topology is also used in numerous applications in which a battery-powered low input voltage is used to generate a high output voltage. At higher power levels, the continuous conduction mode (CCM) boost converter is the preferred topology for a front end with PFC. Thus, in recent years, significant efforts have been made to improve the performance of high-power boost converters. These development efforts have focused on reducing adverse reverse-recovery characteristics that affect the conversion efficiency and the electromagnetic compatibility (EMC) of the boost rectifier.
Generally, reverse-recovery-related losses and EMC problems are minimized by “softly” switching off the boost converter at a controlled turn-off current rate. Many soft-switched boost converters have been proposed that use additional components to form a snubber circuit (passive or active) to control the rate of change of the turn-off current in the boost rectifier. In a passive snubber circuit, only passive components such as resistors, capacitors, inductors, and rectifiers are used. In an active snubber circuit, in addition to the passive elements, one or more active switches are used. Although a passive lossless snubber can improve efficiency, its performance is inadequate to make it useful in high-performance PFC circuit applications. Generally, a passive lossless snubber circuit suffers from increased component stresses and is difficult to operate with soft-switching of the boost switch, which is detrimental in high-density applications that require increased switching frequencies.
Some active snubbers can provide simultaneous reverse-recovery loss reduction and boost switch soft-switching. However, most of these active snubbers offer soft turn-off in the boost rectifier, zero-voltage switching (ZVS) in the boost switch, and “hard” switching in the active-snubber switch. Active-snubbers that implement soft-switching of all semiconductor components (e.g., soft turn-off in the boost rectifier, ZVS in the boost switch, and zero-current switching (ZCS) in the active-snubber switch) are desired.